1. Field of the Invention
The present disclosure relates to measurement technology, and more particularly to a daily checking and calibrating method of a length measuring machine.
2. Discussion of the Related Art
Length measuring machines (TTP) are important optical measurement machines in TFT-LCD manufacturing process. The length measuring machines are mainly for measuring a total pitch of exposure machines while manufacturing the first layer patterns of thin film transistor (TFT) substrate or color filtering (CF) substrates. Generally, the total pitch measurement is conducted by Michelson interferometer, which adopts laser beams with only one frequency to calculate the strength of interference fringes. The stability or intensity of the laser beams, the temperature, or the hardware may result in unstable measurement or serious exceptions. As a result, real characteristics may not be reflected correctly. Furthermore, the exposure machines may be erroneously detected, which may seriously affected the manufacturing process.
Currently, two main suppliers of the above length measuring machines are Spray company and Valve company. The daily checking and calibrating methods of the length measuring machine manufactured by Spray company (“Spray machine”) and the Valve company (“Valve machine) will be described as below.
Regarding the daily checking of the Spray machine, a constant-temperature buffer, which is above the machine, is disposed with a large number of large-scale substrates for daily checking. After the daily check function is activated by operators, the robot transports the large-scale substrate from the constant-temperature buffer to the marked location of the length measuring machine. Normally, the marked locations are identified by engineers at four corners of the large-scale substrate in accordance with the points of the large-scale substrate. After the measurement, the large-scale substrate is then transported back to the constant-temperature buffer.
With respect to the automatic calibration of the Spray machine, a non-segmented glass table is adopted for carrying the substrate. Four corners of the glass table are adhered with cross-shaped marks. During the software initialization, the coordinates of the four cross-shaped marks are calculated and compared with initial coordinates to obtain the calibration coordinates and to update the coordinate system.
The disadvantages of the Spray machine can be concluded as below. The daily checking is not automatically conducted as the daily check function has to be activated by the operators. Also, as the transportation rules of the robot are complex and the robot generally is controlled by different departments, the robot may have to be configured by employees in other departments. Thus, the daily checking cannot be alarmed and handled automatically at the first moment. Upon detecting the exceptions, it is difficult to identify the reasons causing the exceptions, i.e., the exception is caused by the substrate or by the length measuring machine. In addition, the automatic calibration can also be conducted during the software initialization. The automatic calibration cannot be executed at the predetermined time and cannot be executed automatically. However, during the manufacturing process, the length measuring machine has to be in the auto mode, which means that the manual operations or software re-initialization are not allowed. There are also no alarm and prevention mechanism for automatic calibration. When the temperature or the hardware is abnormal the important risk regarding the calibration may occur.
With respect to automatic calibration of the Valve machine, a constant-temperature buffer, which is above the machine, is disposed with a large number of large-scale substrates for daily checking. By activating the daily check function by operators. the robot transports the large-scale substrate from the constant-temperature buffer to the marked location of the machine. Normally, the marked locations are identified by engineers at four corners of the large-scale substrate in accordance with the points of the large-scale substrate. After the measurement, the large-scale substrate is then transported back to the constant-temperature buffer.
The Valve machine has no automatic calibration mechanism. Upon detecting exceptions, the operator has to conduct the daily checking, and then adjusts the coordinate parameters manually until the coordinate parameters meet the specifications.
The disadvantages of the Valve machine can be concluded as below. The daily checking can only be activated by the operators. In addition, as the transportation rules of the robot are complex and the robot generally is controlled by different departments, the robot may have to be configured by employees in other departments. The daily checking cannot be alarmed and handled automatically at the first moment. Upon detecting the exceptions, it is difficult to identify the reasons causing the exceptions, i.e., the exception is caused by the substrate or by the length measuring machine. In addition, the Valve machine does not include automatic calibration mechanism. When performing manual calibration, a large amount of large-scale substrates have to transported to the length measuring machine. The operations are not only complex but also take a longer time, which is about two to four hours. Also, the operator has to be well-experienced. Furthermore, instead of adopting a non-segmented glass table, Valve machine assembles a plurality of glasses to be the glass table on the sample holder. Unlike the Spray machine, the marks of the Valve machine are adheres to the sample holder of the glass table. In the testing process, the unstable sample holder may result in a location difference with ±1 μm. Therefore, the measured values cannot be adopted as reference values. Also, the measured values cannot be adopted to perform the automatic calibration.